Orthopedic surgery utilises many devices such as rods, nails, plates and screws to hold bone together post fracture or fusion or provide stabilisation such as in spinal stabilisation procedures. In children, growth presents a major problem and has historically required multiple surgeries. While rods which have the capacity to lengthen as the patient grows have subsequently been developed, they are not without their problems, in large caused by the fact that they typically rely on a two component system with one rod telescoping into the interior of another rod.
Complications and problems arise in part due to the fact that in a telescoping arrangement, one of the rods must necessarily have a smaller diameter than the other rod. Thus no matter what the material, the moment of inertia of the lesser diametered part of the system is less and can lead to part of the rod bending as the child grows or acutely deforming in a fracture event. Further, while the smaller rod may be cross-locked in some instances with a small K wire, this is a difficult procedure and the resulting rod/wire structure is often not durable.
Further, as the telescopic rods are circular, they do not confer appropriate rotational stability to the system and complications can result from a negative telescoping of the rods.
Another instance of the use of extensible orthopaedic devices is in young patients with spinal deformity. Recent clinical management trends have been to place corrective fixation rods without fusing the spine. These rods can then be adjusted (lengthened) as the child grows to improve final height at the time of definitive fusion.
Growing rod spinal techniques include distraction-based systems and guided growth systems. Although several devices are known, there is a need to provide a stable device which allows for “guided growth” both using the natural growth of the bone being the “motor” for extending the device and using non-natural mechanisms to distract the bone.
In addition to stabilisation and growth of the long bones and the spine, other procedures also call for the use of a device which extends with the bone. In all such cases, it would be desirable to provide a device which is stable and which extends either through the natural growth of the bone or is suitable for use with other “motors” for growth to achieve lengthening of a bone.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form pert of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.